Did my question sound that strange?
I always use the charger that comes with the O2, but I would prefer to bring just one charger with me when I'm on vacation and I already use this USB charger for my cell phones.

Well, the other problem that might arise depending on how much you use both devices each day is which one has priority?

If you charge your O2 overnight, you then will have to charge your cell phone during the day, which may not be good... Your choice of one charger might restrict your ability to use one or both devices. Do you really not have space in your (luggage? baggage? bag?) for a small charger like the O2 has?

In any event, as mentioned in the other forum, make sure your O2 has the hold swich turned on before you plug it in to charge with the mini USB connector.